The present invention relates generally to inks. More particularly, the present invention relates to color imparting compositions for ink jet printer inks and inks formulated with same that are useful for printing machine readable indicia, such as postage.
The Information-Based Indicia Program (IBIP) is a distributed trusted system originally proposed by the United States Postal Service (USPS). The IBIP requires printing large, high density, two dimensional (2-D) bar codes on mail pieces. The Postal Service expects the IBIP to provide cost-effective assurance of postage payment for each mail piece processed. However, such assurance is only as good as the printing and verification process within the IBIP.
Verification of Information-Based Indicia (IBI) is the process of proving that the postage evidenced on each IBI mail piece has been paid. A digital signature scheme has been devised to provide such evidence. The digital signature scheme for the IBI system provides a secure method of proving the validity, specifically the integrity and authenticity, of the data within the indicia. For the verification system to work efficiently, the indicia printed on an envelope constituting postage must be machine readable.
Postal indicia or franking machines have been developed that use digital printing technology to permit the use of variable information in postal indicia and to provide enhanced printing resulting in better indicia print quality. Better print quality of the postal indicia enables the postal indicia to be more efficiently read by optical character recognition equipment, bar code readers and other types of machine vision technology typically used in automatic sorting and postage verification machines. Poor print quality, in terms of precision and contrast, of the indicia printed on an envelope results in inefficient processing of mail pieces and leads to higher processing costs.
The introduction of digital printing technology for printing indicia or franking is limited, to some extent, by the limited existence of inks that are suitable for franking, and at the same time, are functional with specific ink jet technology. Piezoelectric ink jet inks which are water fast use different organic solvents, such as tripropylene glycol methyl ether or other glycol ethers, instead of water to improve the water fastness. The organic solvents are preferred because they dissolve or disperse colorants that are insoluble in water. However, ink jet printers contain a substantial number of parts, such as the inker foam, cartridge housing and printer base, made with plastic materials such as acrylonitrile styrene (AS), polymethylmethacrylate (PMMA), and acrylonitrile butadiene styrene (ABS). These plastics may be somewhat soluble in the preferred organic solvents, and therefore, the organic solvents in the inks could cause the plastic parts to fail. Accordingly, water is generally used as the ink solvent because the plastic ink jet printer parts are not soluble therein.
After the implementation of the IBIP, inks which met the requirements for franking and machine readability, among other specifications, and were suitable for printing postal indicia with bubble jet or piezoelectric technology, were no longer suitable because such inks have a relatively high xe2x80x9credxe2x80x9d reflectance. For example, some inks that were suitable prior to IBIP, but no longer suitable after IBIP, used reactive black 31 or C.I. direct black 195 dyes as a black colorant materials. Prior art dyes using such materials as colorants do not necessarily have light absorbency characteristics that efficiently match the characteristics of scanners in the optical character readers that are now used by the postal services to read the printed postal indicia under the IBIP. These scanners typically include a red light filter, which is generally adapted to have a maximum for light transmission at about 630 nm and, in some cases a green light filter, which is generally adapted to have a maximum for light transmission at about 550 nm.
To determine the contrast signal for an indicia printed on a substrate, a Print Reflectance Difference (PRD) test has been devised. The PRD is the difference between the reflectance of the unprinted part of the substrate and the reflectance of the printed part of the substrate, as measured with a United States Postal Service Envelope Reflectance (ER) Meter. The USPS ER meter has green and red light filters. In ink jet inks which use these black colorant materials alone to provide color, the PRD values have been known to vary between 2.8 to 30 percent. Under the IBIP, such variations in Print Reflectance Difference values can cause longer read times to decode indicia because the print contrast varies so widely. The longer indicia read times lowers the overall efficiency of processing such indicia, and therefore, increases the cost of processing mail bearing such indicia.
It is therefore desirable to produce a color imparting composition for an ink which is suitable for use in an ink jet printer which has a low light reflectance (strong absorbency) when applied to a substrate in the wavelength range utilized by the optical character recognition devices which are used to scan such printed postage indicia.
In accordance with the present invention, colorant compositions for making ink jet printer inks which can be used to print machine readable indicia, such as postal indicia, are provided. The color imparting compositions generally comprise a water soluble black colorant material adapted to absorb light in a wavelength range between about 400 to 650nm, and a water soluble cyan colorant material having a molar extinction coefficient of at least 10,000 at a wavelength maximum in the range of about 580 to 750 nm. When used in an ink jet printer ink composition, the color imparting compositions yield an ink which has a low reflectivity of light in the wavelength regions typically used by the scanners incorporated in postage reading machines.